Lifts - of all types: Google "Burr Lift".
The Burr lifts (and others) lift a person from the ground to the height of the RV - normally attached to the side of the RV by the steps.
Lifts for a handicapped scooters (etc.) you have seen... there are many options (12V operated), so no physical lifting req'd.
The Newmar MH mentioned by a poster is expensive! If you can afford it, it's specifically designed for wheelchair use. (IIRC) there is at least one other mfgr of same.
If you want an *inexpensive* travel trailer - look at toy haulers - which have a ramp. At least one mfgr has a side (rather than rear) ramp.